1. Field of the Invention
The invention relates to a hydraulically controlled clutch actuation device and in particular to an improvement which provides, among other things, an improvement of the reliability of the overall system and an increased life of the hydraulic jack controlling the displacement of the clutch release bearing.
2. Description of the related art.
Hydraulically controlled clutch systems are known. An actuation device of this kind is generally made up of two main assemblies: the conventional clutch release bearing and a hydraulic jack which acts on the release bearing in order to displace it along the output shaft of the clutch, the bearing being coupled to the actuator of the clutch which in most cases is an annular metal diaphragm. The clutch release bearing is slidably mounted on a fixed sleeve rigid with the gear box and surrounding the input shaft of the latter which is also the clutch output shaft. The jack is arranged around this fixed sleeve and comprises an annular chamber filled with incompressible fluid and a piston, which has an overall tubular and cylindrical shape, coupled to the clutch release bearing. A system of this kind is disclosed, for example, in European Patent Application No. 0 146 283. In this device, the inner surface of the jack chamber is defined by the outer surface of the fixed sleeve which makes it necessary to machine a considerable length of the sleeve. In addition, if oil leaks from the jack it may spread along this fixed sleeve to the clutch itself, which may lead to severe damage. In addition, dirt may infiltrate the chamber, particularly when the fixed sleeve is worn, which may be detrimental to the correct operation of the jack.
The object of the invention is to remedy these drawbacks of the known apparatus.